1. Field of the Invention
The present invention relates to a light source device for an endoscope and an endoscope system.
2. Description Related to the Prior Art
In medical fields, diagnoses using endoscope systems are widely performed. The endoscope system comprises a light source device for an endoscope (hereinafter simply referred to as the light source device), an endoscope, and a processor device. The light source device generates illumination light with which an object of interest (hereinafter simply referred to as the object, e.g. mucosa or the like in a body cavity) is to be irradiated. Observation modes of the endoscope system offer normal observation, in which normal light (white light) is used as the illumination light, and various types of special observation, in which special light is used as the illumination light. The observation of oxygen saturation levels (hereinafter referred to as the oxygen saturation observation) is one form of the special observation.
The oxygen saturation observation is a method of observation in which oxygen saturation levels, which indicate how much oxygen is contained in blood vessels, are calculated and an image representing the oxygen saturation levels is displayed. The oxygen saturation observation is performed by using light (measurement light) whose wavelength range is limited to 450 to 500 nm based on the fact that a difference between the absorption coefficients of oxyhemoglobin and deoxyhemoglobin, which are contained in blood vessels, is large in the wavelength range of 450 to 500 nm (see US2012/0157768 (corresponding to Japanese Pat. No. 5303012)).
It has been suggested to reduce the intensity of the normal light (the white light) in a wavelength range of 460 to 500 nm to prevent the reduction in contrast (hereinafter referred to as the blood vessel contrast) between the mucosal surface and the blood vessels in the normal observation. This is based on the fact that a difference in reflectance between the blood vessel and the mucosa surrounding the blood vessel is small in the wavelength range greater than or equal to 460 nm (see US2011/0288387 (corresponding to Japanese Pat. No. 5306447)). Thereby, the blood vessel contrast in the image is increased.
A broadband light source such as a xenon lamp, a white LED (Light Emitting Diode), or the like is used as the light source device. Recently, a combination of semiconductor light sources of different colors (e.g. a blue LED, a green LED, and a red LED) has been used. A blue LED having a peak wavelength around 450 to 460 nm is used as a blue light source.
As described in the US2012/0157768 and the US2011/0288387, the illumination light in the wavelength range of 450 to 500 nm is used for the oxygen saturation observation, whereas the intensity of the illumination light in the wavelength range of 460 to 500 nm is reduced in the normal observation to increase the blood vessel contrast. In other words, the blue illumination light for the normal observation differs in wavelength from that for the oxygen saturation observation. For this reason, it is necessary to use different light sources for the normal observation and the oxygen saturation observation, respectively. The two types of observation cannot be performed by using a single endoscope system.